I hope you are well today and thank you for your question.
This is a theme specific issue that you are using on your site.
You can resolve this by adding the below CSS code in the Custom CSS option of Ivory Search plugin settings on the path Ivory Search -> Settings -> Settings
@media screen and (max-width: 980px){
.is-menu.dropdown form#searchform {
display: block;
position: static;
float: left;
min-width: 270px;
}
#et-top-navigation .is-menu > a {
display: none;
}
#et-top-navigation li.is-menu {
background: none !important;
height: 0;
width: 0;
}
}
Best regards,
Ivory Search Support